Space charge non-contact test system and method

Abstract

The present invention provides a space charge non-contact test system and method, the system includes: a substrate, a mobile platform, a bracket, a piezoelectric drive element, an electric field excitation electret layer, an insulating medium to be tested, a field balance electret layer, a piezoelectric sensor array, an absorbing material layer, a multi-way control switch, a preamplifier, an integrated shielding electrode, a low-voltage pulse generator, an oscilloscope and a computer; a non-contact test is performed on the space charge inside the insulating medium to be tested by driving the polarized electret layer with a low-power pulse voltage to generate a high-intensity alternating pulse field; and a layered scanning and reconstruction of the original space charge in the insulating medium is performed by confining the space charge layer by balancing the polarized electret field. Compared with the prior art, the present invention improves the test accuracy and sensitivity of the outer layer, shallow layer and deep layer space charge of the insulating medium to be tested, and has the ability to test the space charge of the insulating medium of the spacecraft protective layer in a space environment.

Description

Technical Field

[0001] The present invention relates to the field of space charge testing technology, in particular to a space charge non-contact testing system and method, and in particular to a space charge non-contact testing system and method based on electret field confinement induction. Background Art

[0002] The formation of deposited space charge inside insulating dielectric materials is caused by the environment during preparation or application, such as micro-nano processing based on high-energy beam / electron beam / plasma, on-orbit operation of spacecraft, high-voltage DC electric field, high-speed friction between high-dynamic carriers and air, etc., which will introduce charge and store it in the body. Domestic and foreign studies have shown that the generation and accumulation of space charge will distort the electric field distribution in insulating dielectric materials, and under some harsh conditions, it will cause aging and breakdown of insulating dielectric materials, reduce or even destroy the electrical properties of the materials; in addition, this abnormal charge accumulation will also discharge other conductors in the system, causing damage and failure of key electronic components or circuits of electronic systems, which is extremely harmful.

[0003] Currently, there are several methods for testing space charge: Thermally Stimulated Current (TSC), Thermally Stimulated Surface Potential (TSSP), Thermo Luminescence (TL), Piezo-electric Induced Pressure Wave Propagation (PIPWP), Laser Induced Pressure Propagation (LIPP) and Pulsed Electro-Acoustic (PEA).

[0004] In the existing space charge testing technology, the PEA method is generally used to measure the space charge distribution of insulating dielectric materials. The basic principle is: when there is space charge in the insulating medium, the high-voltage electric pulse applied to both ends of the insulating medium will cause the vibration of the space charge inside the insulating medium to generate pressure waves, and then these pressure waves are converted into electrical signals through piezoelectric sensors, where the amplitude of the electrical signal reflects the size of the space charge density, and the time it takes to reach the piezoelectric sensor reflects the distribution of the space charge inside the sample.

[0005] The PEA method is very mature in the test of space charge of traditional high-voltage insulated cables, but there are few reports on the test of space charge of spacecraft in orbit. Affected by the irradiation of high-energy particle beams in space, the insulating medium of the spacecraft in orbit will also accumulate space charge, which seriously endangers the normal operation of the spacecraft. However, the traditional PEA device requires that the excitation electrode must be in a contact configuration that fits tightly with the sample during the test. This configuration directly blocks the irradiation of the sample by the high-energy particle beam in space, and it is impossible to realize the space charge on-orbit test of the spacecraft insulating medium; the traditional PEA device requires a high-voltage pulse power supply as an excitation, which is impossible in spacecraft with extremely tight energy ratio; the traditional PEA device has serious interface effects and cannot test the outer and shallow space charge of the sample, which is extremely important in the study of spacecraft charging and discharging effects; the traditional space charge test results are a comprehensive reflection of the mutual influence of space charge at various positions in the sample, and cannot reflect the real space charge distribution of specific layers inside the sample. In summary, for the space charge test of the insulating medium of the spacecraft shield layer, it is necessary to explore a non-contact testing system and method for the space charge of the insulating medium of the spacecraft shield layer, which can realize the layered scanning and reconstruction of the original space charge in the insulating medium under the drive of a low-power power supply voltage.

[0006] Patent document CN106018987A discloses a space charge test system and test method applied to the field of high-voltage cable testing, wherein the space charge test system comprises: a copper electrode arranged on the upper surface of the test table, a shielding cover for shielding the copper electrode, and a copper conductor with one end connected to the copper electrode and the other end passing through the shielding cover; a cable limiter for fixing the cable sample; a first shielding box installed on the lower surface of the test table and facing the copper electrode, and a first piezoelectric sensor, a first aluminum foil, and a first organic glass block arranged in the first shielding box from top to bottom; a second shielding box installed on the lower surface of the test table and facing the cable limiter, and a second piezoelectric sensor, a second aluminum foil, and a second organic glass block arranged in the second shielding box from top to bottom; and a signal amplifier for receiving electrical signals sent by the first piezoelectric sensor and the second piezoelectric sensor. However, this method does not solve the problem of space charge testing of the insulating medium of the spacecraft shielding layer. Summary of the invention

[0007] In view of the defects in the prior art, an object of the present invention is to provide a space charge non-contact testing system and method.

[0008] According to a space charge non-contact testing system provided by the present invention, the system comprises:

[0009] Substrate, mobile platform, bracket, piezoelectric drive element, electric field excitation electret layer, insulating medium to be tested, field balance electret layer, piezoelectric sensor array, absorbing material layer, multi-way control switch, preamplifier, integrated shielding electrode, low voltage pulse generator, oscilloscope and computer;

[0010] One end of the substrate is mechanically connected to the mobile platform, and the substrate is parallel to the upper surface of the insulating medium to be tested; the upper surface of the piezoelectric driving element is mechanically connected to the substrate and vibrates under the electrical excitation of the low-voltage pulse generator; the electric field excitation electret layer is mechanically insulated and connected to the lower surface of the piezoelectric driving element, and an alternating pulse electric field is generated under the excitation of the piezoelectric driving element; the field balance electret layer is spin-coated on the upper surface of the integrated shielding electrode, which is used to place the insulating medium to be tested and form a balanced electric field; the piezoelectric sensor array is equidistantly placed on the lower surface of the integrated shielding electrode, which is used to receive the acoustic pressure waves induced by the space charge of the insulating medium to be tested under the action of the alternating pulse field generated by the electric field excitation electret layer The signal is converted into an electrical signal; the absorbing material layer is used to absorb the acoustic pressure wave signal passing through the piezoelectric sensor array to reduce reflection; the multi-way control switch is used to control the on-off sequence between a single piezoelectric sensor and the preamplifier; the preamplifier is placed inside the integrated shielding electrode and is electrically connected to the piezoelectric sensor array to amplify the electrical signal data output by the piezoelectric sensor; the oscilloscope is electrically connected to the preamplifier to collect and display the amplified electrical signal data and transmit it to the computer through the serial port; the computer analyzes, processes and reconstructs the collected electrical signal data to obtain the spatial charge distribution information of the insulating medium.

[0011] Preferably, the distance between the substrate and the surface of the insulating medium to be measured is adjusted by moving the platform.

[0012] Preferably, the electric field excitation electret layer is used as an alternating pulse electric field generator to induce space charge to generate acoustic pressure waves, including a back electrode and an electret layer film spin-coated on the back electrode using micro-nano technology, and the surface of the electret layer film has polarized charges.

[0013] Preferably, the array distribution of the piezoelectric sensors realizes three-dimensional measurement of the space charge of the insulating medium to be measured.

[0014] Preferably, the field-balancing electret layer is spin-coated on the upper surface of the integrated shielding electrode using a micro-nano process, and is used to place the insulating medium to be measured and form a balanced electric field to confine the space charge layer to be measured.

[0015] A space charge non-contact testing method provided by the present invention is applicable to the above-mentioned space charge non-contact testing system, and the method comprises:

[0016] Step 1: Using a first pulse voltage to drive the electric field excitation electret layer suspended on the insulating medium to be tested to vibrate and generate an alternating pulse field, so that the space charge in the insulating medium to be tested generates an acoustic pressure wave, thereby realizing a non-contact test of the space charge inside the insulating medium to be tested;

[0017] Step 2: A balanced electrostatic field in the opposite direction to the alternating pulse field is formed by placing a field-balancing electret layer under the insulating medium to be tested, thereby forming a zero-field strength interface inside the insulating medium to be tested, thereby realizing a layered scanning reconstruction of the space charge inside the insulating medium to be tested.

[0018] Preferably, the polarization charges on the surface of the electret layer film of the field balance electret layer generate a balanced electrostatic field.

[0019] Preferably, the non-contact test comprises an integral test, the integral test comprising:

[0020] Step 101: polarizing the electret layer film on the electric field excited electret layer, so that polarized charges are generated on the surface of the electret layer film, and obtaining a first polarized charge density;

[0021] Step 102: placing the insulating medium to be tested on the electret layer film surface of the field balance electret layer, adjusting the distance between the electric field excitation electret layer and the insulating medium to be tested, and obtaining the distance between the upper surface of the insulating medium to be tested and the lower surface of the field balance electret layer;

[0022] Step 103: Using a low voltage pulse generator and a piezoelectric vibration element, an electric field is excited to excite the electret layer to vibrate, thereby generating an alternating pulse electric field;

[0023] Step 104: The space charge in the insulating medium to be tested generates an acoustic pressure wave through the alternating pulse electric field, and the space charge signal window in the insulating medium to be tested is determined on the oscilloscope through the acoustic pressure wave signal;

[0024] Step 105: The data collected by the oscilloscope is transmitted to a computer, and the computer analyzes and processes the collected signals to obtain the distribution information of the overall space charge of the insulating dielectric material.

[0025] Preferably, the on-off sequence between different piezoelectric sensors and the preamplifier is controlled by on-off of a multi-way control switch to achieve three-dimensional measurement of the overall space charge of the insulating medium to be measured.

[0026] Preferably, the non-contact test includes a layered scanning and reconstruction test, and the layered scanning and reconstruction test includes:

[0027] Step 201: polarizing the electret layer film on the electric field excited electret layer, so that polarized charges are generated on the surface of the electret layer film, and obtaining a first polarized charge density;

[0028] Step 202: polarizing the electret layer film on the field balance electret layer to generate polarized charges on the surface of the electret layer film, thereby obtaining a second polarized charge density;

[0029] Step 203: placing the insulating medium to be tested on the electret layer film surface of the field balance electret layer, adjusting the distance between the electric field excitation electret layer and the insulating medium to be tested, and obtaining the distance between the upper surface of the insulating medium to be tested and the lower surface of the field balance electret layer;

[0030] Step 204: Calculate the zero-field intensity interface position inside the insulating medium to be tested;

[0031] Step 205: Using a low voltage pulse generator and a piezoelectric vibration element, an excitation electric field excites the electret layer to vibrate, thereby generating an alternating pulse electric field;

[0032] Step 206: generating an acoustic pressure wave between the upper surface of the insulating medium to be tested and the zero field strength interface position by means of an alternating pulse electric field, and determining a space charge signal window in the insulating medium to be tested by means of the acoustic pressure wave signal on an oscilloscope;

[0033] Step 207: The data collected by the oscilloscope is transmitted to a computer, and the computer analyzes and processes the collected signals to obtain the distribution information of the overall space charge of the insulating dielectric material;

[0034] Step 208: controlling the on-off sequence between different piezoelectric sensors and the preamplifier by turning on and off the multi-way control switch to achieve three-dimensional measurement of the local space charge of the insulating medium to be measured;

[0035] Step 209: reducing the second polarization charge density of the electret layer film on the field balance electret layer to adjust the zero field intensity interface position;

[0036] Step 210: Repeat steps 201 to 209 to test the space charge in the entire insulating medium to be tested;

[0037] Step 211: Reconstruct the space charge information of each layer through a computer to obtain the distribution information of the space charge of the insulating medium to be tested.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The present invention drives the electric field suspended on the insulating medium to be tested by low-power pulse voltage to stimulate the high-frequency vibration of the electret layer to produce a high-intensity alternating pulse field, thereby inducing the space charge in the insulating medium to generate acoustic pressure waves. This low-voltage driving of the electret layer to produce a high-intensity alternating pulse field makes the non-contact configuration of the space charge test device possible, and also provides a feasible solution for the on-orbit test of the space charge of the insulating medium of the spacecraft protective layer.

[0040] 2. The present invention also has a balanced electret layer below the insulating medium. The direction of the balanced field formed by the electret is opposite to the above-mentioned alternating pulse field. The interaction between the two electret fields will form a zero field strength interface at a certain position inside the insulating medium. The position of the interface can be controlled by adjusting the size of the balanced electret field. The existence of the zero field strength interface prevents the alternating pulse field from crossing the zero field strength interface to act on other positions of the insulating medium. The balanced field on one side of the zero field strength interface will firmly confine the space charge in the area. In this way, the space charge layer that is not confined by the balanced field can generate acoustic pressure waves under the induction of the alternating pulse field, thereby achieving the purpose of layered scanning and reconstruction of the original space charge in the insulating medium of the spacecraft protective layer driven by a low-power power supply voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0042] Figure 1 It is a structural schematic diagram of the present invention;

[0043] Figure 2 It is a schematic diagram of the distribution of the piezoelectric sensor array of the present invention;

[0044] Figure 3a It is the integrated test principle diagram of the present invention;

[0045] Figure 3b is a schematic diagram of an acoustic pressure wave signal of the present invention;

[0046] Figure 4a This is a schematic diagram of the hierarchical scanning and reconstruction test of the present invention;

[0047] Figure 4b Schematic diagram of another acoustic pressure wave of the present invention.

[0048] Reference numerals:

[0049] 1: substrate; 2: mobile platform; 3: bracket; 4: piezoelectric driving element; 5: electric field excitation electret layer; 6: insulating medium to be measured; 7: field balance electret layer; 8: piezoelectric sensor array; 9: absorbing material layer; 10: multi-way control switch; 11: integrated shielding electrode; 12: preamplifier; 13: low voltage pulse generator; 14: oscilloscope; 15: computer. DETAILED DESCRIPTION

[0050] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0051] Figure 1 It is a structural schematic diagram of the present invention, such as Figure 1 As shown, the present invention provides a space charge non-contact testing system, which includes: a substrate 1, a mobile platform 2, a bracket 3, a piezoelectric driving element 4, an electric field excitation electret layer 5, an insulating medium to be tested 6, a field balance electret layer 7, a piezoelectric sensor array 8, an absorbing material layer 9, a multi-way control switch 10, an integrated shielding electrode 11, a preamplifier 12, a low-voltage pulse generator 13, an oscilloscope 14 and a computer 15.

[0052] Specifically, the substrate is in the shape of a flat plate and made of aluminum alloy. One end of the substrate is mechanically connected to a moving platform. The substrate is parallel to the upper surface of the insulating medium to be measured, and the distance between the substrate and the surface of the insulating medium to be measured is adjusted by the moving platform. The upper surface of the piezoelectric driving element is mechanically connected to the substrate and vibrates under the electrical excitation of a low-voltage pulse generator. The electric field excitation electret layer serves as an alternating pulse electric field generating source for inducing space charges to generate acoustic pressure waves, including a back electrode and an electret layer film spin-coated on the back electrode using a micro-nano process. The surface of the electret layer film has polarized charges. The electric field excitation electret layer is mechanically insulated and connected to the lower surface of the piezoelectric driving element, and an alternating pulse electric field is generated under the excitation of the piezoelectric driving element. The field balancing electret layer is spin-coated on the upper surface of the integrated shielding electrode for placing the insulating medium to be measured and forming a balanced electric field. The piezoelectric sensor array is equidistantly placed on the lower surface of the integrated shielding electrode. The surface is used to receive the acoustic pressure wave signal induced by the space charge of the insulating medium to be measured under the action of the alternating pulse field generated by the electric field exciting the electret layer and convert it into an electrical signal; the array distribution of the piezoelectric sensor can realize the three-dimensional measurement of the space charge of the insulating medium; the absorbing material layer is used to absorb the acoustic pressure wave signal passing through the piezoelectric sensor array to reduce reflection; the multi-way control switch is used to control the on-off sequence between a single piezoelectric sensor and the preamplifier; the preamplifier is placed inside the integrated shielding electrode and is electrically connected to the piezoelectric sensor array to amplify the electrical signal data output by the piezoelectric sensor; the oscilloscope is electrically connected to the preamplifier to collect and display the amplified electrical signal data and transmit it to the computer through the serial port; the computer analyzes, processes and reconstructs the collected electrical signal data to obtain the space charge distribution information of the insulating medium.

[0053] Specifically, the electric field excites the electret layer as an alternating pulse electric field source for inducing space charges to generate acoustic pressure waves, including a back electrode and an electret layer film spin-coated on the back electrode using a micro-nano process, and the surface of the electret layer film has polarized charges.

[0054] The electret layer film includes an electret matrix and polarization charges on its surface.

[0055] Specifically, the electret layer film is a polarized electret layer film, and the substrate of the polarized electret layer film adopts one of polyethylene terephthalate (PET), polypropylene (PP) and polyethylene naphthalate diformic acid glycol ester (PEN); the film is formed on the back electrode by micro-nano technology: the material of the electret layer film is coated on the back electrode by spin coating process; the surface of the electret substrate is polarized to have polarization charge, so as to form the electret layer film.

[0056] It is known that the surface of the polarized electret layer film has polarized charges, and the electric field excites the electret layer to be mechanically insulated and connected to the lower surface of the piezoelectric driving element, and an alternating pulse electric field can be generated under the excitation of the piezoelectric driving element.

[0057] Specifically, the surface of the electret layer film has polarized charge through polarization. The electret polarization method includes: using radiation ionization or corona discharge to generate positive and negative charges in the air above the substrate of the electret layer film, then the back electrode of the electret layer is grounded, and under the action of an external bias polarization high-voltage electric field, the positive and negative opposite charges are driven to separate and accelerate, and injected into the electret layer film of the electret layer; the polarity of the electret unit after polarization is opposite to the polarity of the back electrode of the electret unit during polarization. When stationary, the polarized charge on the surface of the electret layer film can form a strong electrostatic field in a direction perpendicular to the electret surface, and the electric field strength increases with the increase of the polarized charge density. As the piezoelectric drive element vibrates, the electret layer is excited to vibrate at a high frequency, and the polarized charge layer generates an alternating pulse electric field under high-frequency motion.

[0058] Furthermore, the space charge in the insulating medium to be tested is disturbed under the action of the alternating pulse electric field to form an acoustic pressure wave. The intensity of the alternating pulse electric field acting on the insulating medium to be tested depends on the properties of the insulating medium material to be tested, the air gap and the properties of the electret layer film itself, such as thickness, dielectric constant and surface potential.

[0059] Furthermore, it also includes a balanced electrostatic field generated by polarization charges on the surface of the electret layer film of the field balance electret layer.

[0060] It is known that when the surface of the field-balancing electret layer film on the integrated shielding electrode has a polarization charge with the opposite polarity to that of the electric field-excited electret layer film, the balanced electrostatic field is consistent with the direction of the strong electrostatic field of the electric field-excited electret layer film, which plays an auxiliary enhancement role in the alternating pulse electric field. When the surface of the field-balancing electret layer film on the integrated shielding electrode has a polarization charge with the same polarity as that of the electric field-excited electret layer film, the balanced electrostatic field is opposite to the direction of the strong electrostatic field of the electric field-excited electret layer film, and the interaction between the two electrostatic fields will form a zero field strength interface at a certain position inside the insulating material to be tested. The existence of the zero field strength interface prevents the effect of the alternating pulse electric field from crossing the zero field strength interface to reach other positions of the insulating dielectric material to be tested.

[0061] Furthermore, by adjusting the size of the field-balancing electret field, the position of the zero-field-strength interface can be controlled. The balanced field on one side of the zero-field-strength interface will firmly confine the space charge in that area. The space charge layer of the insulating medium that is not confined by the balanced field will generate acoustic pressure waves under the induction of the alternating pulse field, thereby realizing layered scanning and reconstruction of the original space charge in the insulating medium.

[0062] Among them, the array distribution of piezoelectric sensors realizes the three-dimensional measurement of the space charge of the insulating medium to be measured.

[0063] In the present invention, the piezoelectric driving element 4 uses the inverse piezoelectric effect as a vibration source, and the vibration frequency range is 1Hz to 1000MHz; the voltage amplitude of the low-voltage pulse generator 13 is 60V to 300V, and the pulse width is 10 nanoseconds (ns); the mobile platform 2 is specifically a manual precision fine-tuning displacement stage with a range of 0 to 20mm, and is installed on the upper surface of the integrated shielding electrode 11 through the bracket 3.

[0064] Figure 2 Schematic diagram of the piezoelectric sensor array distribution of the present invention, as shown in Figure 2 As shown, the piezoelectric sensor array 8 specifically adopts a PVDF piezoelectric film sensor with a thickness of 28 μm and an area of ​​1 cm×1 cm. The distribution of the piezoelectric sensor array 8 in the present invention is as follows: Figure 2 As shown, 16 piezoelectric sensors are placed on the lower surface of the integrated shielding electrode 11 in a 4×4 distribution manner with equal spacing, and the spacing between each piezoelectric sensor is 2 mm.

[0065] Specifically, the field-balancing electret layer is spin-coated on the upper surface of the integrated shielding electrode using a micro-nano process, and is used to place the insulating medium to be measured and form a balanced electric field to confine the space charge layer to be measured.

[0066] In the present invention, the electret layer film of the electric field excitation electret layer is a rectangular film with a width of w, a length of l, and a thickness of d. The electric field excitation electret layer film is polarized by ionization or corona discharge, so that the surface of the electric field excitation electret layer film has polarized charges. The surface potential V of the electret after polarization is measured by a surface potential measuring instrument. e , the surface charge of the electret is Q e , the surface charge density is σ e , the conversion relationship between different physical quantities is shown in formula (1) and formula (2):

[0067]

[0068]

[0069] Where ε0 represents the dielectric constant in vacuum, ε e Represents the relative dielectric constant of the electret material.

[0070] Figure 3a It is the integrated test principle diagram of the present invention, such as Figure 3a As shown, it includes: an integrated shielding electrode 11, a piezoelectric driving element 4, an electric field excitation electret layer 5, an insulating medium to be measured 6 and a field balance electret layer 7; the thickness of the insulating medium to be measured 6 is d1, the distance between the positive space charge 61 inside it and the upper surface of the insulating medium to be measured 6 is x1, and the distance between the negative space charge 62 inside it and the upper surface of the insulating medium to be measured 6 is x2; the electric field excitation electret layer 5 has a polarization charge 51 by polarizing its surface, the polarity is positive, and the surface potential is V e1 ; When stationary, the air gap height between the electric field excitation electret layer 5 and the insulating medium 6 to be measured is d2; under the joint action of the positive space charge 61 and the negative space charge 62 inside the insulating medium to be measured, the upper surface of the field balance electret layer 7 film induces an induced charge 71, assuming that the polarity is negative, and the corresponding lower surface induces an induced charge 72, assuming that the polarity is positive; under the action of the low-voltage pulse generator 13, the electret layer 5 is excited to vibrate at high frequency together with the piezoelectric driving element 4, and the polarized charge 51 generates an alternating pulse electric field E1 in the normal direction of its surface under high-frequency reciprocating motion. The alternating pulse electric field E1 can be expressed by formula (3):

[0071]

[0072] Wherein, δ represents the maximum displacement of the movement; r represents the distance from the lower surface of the electric field excited electret layer 5; ε r It represents the equivalent relative dielectric constant of the air gap and the insulating dielectric material layer to be tested.

[0073] Figure 3b is a schematic diagram of an acoustic pressure wave signal of the present invention, such as Figure 3b As shown in the figure, the horizontal axis is time and the vertical axis is pressure P(t). Specifically, the space charge in the insulating medium to be measured is disturbed under the action of the alternating pulse electric field to generate an acoustic pressure wave. The acoustic pressure wave generated by the space charge close to the piezoelectric sensor is received first. Therefore, the acoustic pressure wave signals of each charge layer reaching the piezoelectric sensor are P 72 , P 71 , P 62 and P 61 , the intensity of the acoustic pressure wave signal is expressed by pressure, which can be calculated by formula (4):

[0074] P(t)=σ·E1(t); (4)

[0075] Where σ represents the space charge density at a certain position in the insulating medium to be measured.

[0076] Furthermore, taking the piezoelectric sensor in the piezoelectric sensor array as a polyvinylidene fluoride (PVDF) piezoelectric film sensor as an example, the acoustic pressure wave is transmitted to the piezoelectric sensor in the piezoelectric sensor array. Due to the piezoelectric effect, the output voltage of the PVDF piezoelectric film sensor satisfies formula (5):

[0077]

[0078] Where a represents the thickness of the PVDF piezoelectric film sensor; d 33 Represents the piezoelectric strain constant of the piezoelectric sensor in the thickness (longitudinal) direction; ε rp It is known from formula (5) that the voltage generated by the acoustic pressure wave P(t) is only related to the thickness of the piezoelectric sensor and has nothing to do with the surface area of ​​the PVDF piezoelectric film sensor.

[0079] Figure 4a This is a schematic diagram of the hierarchical scanning and reconstruction test of the present invention, such as Figure 4a As shown, it includes: an integrated shielding electrode 11, a piezoelectric driving element 4, an electric field excitation electret layer 5, an insulating medium to be measured 6 and a field balance electret layer 7; the thickness of the insulating medium to be measured 6 is d1, the distance between the positive space charge 61 inside it and the upper surface of the insulating medium to be measured 6 is x1, and the distance between the negative space charge 62 inside it and the upper surface of the insulating medium to be measured 6 is x2; the electric field excitation electret layer 5 has a polarization charge 51 on its surface through polarization, the polarity is positive, and the surface potential is V e1 ; When stationary, the air gap height between the electric field-excited electret layer 5 and the insulating medium 6 to be tested is d2; under the action of the low-voltage pulse generator, the electret layer 5 is excited to vibrate at high frequency along with the piezoelectric vibration element 4, and the polarized charge 51 generates an alternating pulse electric field E1 in the normal direction of its surface under high-frequency reciprocating motion.

[0080] Furthermore, the field balance electret layer 7 is a rectangular film with a width of w s , the length is l s , thickness is d s The field balance electret layer 7 is polarized by using ionization or corona discharge to make the surface of the film have polarization charge 73, and the surface potential V of the electret after polarization is measured by using a surface potential measuring instrument. es , the surface charge of the electret is Q es , the surface charge density is σ es , the lower surface of the induced charge 74 is negative. The direction of the electric field E2 of the polarized charge 73 acting on the insulating dielectric material 6 is opposite to that of E1, and its field strength can be expressed as formula (6):

[0081]

[0082] Among them, r s represents the distance from the upper surface of the field-balancing electret layer 7 .

[0083] Figure 4b is a schematic diagram of another acoustic pressure wave of the present invention, such as Figure 4b As shown, the horizontal axis is time and the vertical axis is pressure P(t). Under the joint action of E1 and E2, there is a zero field interface 63, the position of which can be determined by E1=E2, formula (3) and formula (6). Considering the influence of the zero field interface 63, the action area of ​​the alternating pulse electric field is limited to between the zero field interface 63 and the upper surface of the insulating medium 6 to be tested. Only the space charge 61 located in this area can be disturbed under the action of the alternating pulse electric field to generate an acoustic pressure wave P 61 .

[0084] The present invention also provides a space charge non-contact testing method, which is applicable to the above-mentioned space charge non-contact testing system and comprises the following steps:

[0085] Step 1: Using a first pulse voltage to drive the electric field excitation electret layer suspended on the insulating medium to be tested to vibrate and generate an alternating pulse field, so that the space charge in the insulating medium to be tested generates an acoustic pressure wave, thereby realizing non-contact testing of the space charge inside the insulating medium to be tested.

[0086] Step 2: A balanced electrostatic field in the opposite direction to the alternating pulse field is formed by placing a field-balancing electret layer under the insulating medium to be tested, thereby forming a zero-field strength interface inside the insulating medium to be tested, thereby realizing a layered scanning reconstruction of the space charge inside the insulating medium to be tested.

[0087] Among them, the first pulse voltage is a low-power pulse voltage.

[0088] Specifically, firstly, a low-power pulse voltage is used to drive the electric field excitation electret layer suspended on the insulating medium to be tested to vibrate at high frequency to generate a high-intensity alternating pulse field, thereby inducing the space charge in the insulating medium to generate acoustic pressure waves, so as to complete the non-contact test of the space charge inside the insulating medium; then, a balanced electrostatic field in the opposite direction to the alternating pulse field is formed by a field-balancing electret layer placed under the insulating medium to be tested, thereby forming a zero-field strength interface at a certain position inside the insulating medium to be tested. The existence of the zero-field strength interface prevents the alternating pulse field from crossing the zero-field strength interface to act on other positions of the insulating medium to be tested, and the balanced electrostatic field on one side of the zero-field strength interface will firmly confine the space charge in this area, and the space charge layer that is not confined by the balanced field can generate acoustic pressure waves under the induction of the alternating pulse field, thereby realizing the layered scanning and reconstruction of the original space charge in the insulating medium to be tested.

[0089] The polarized charges on the surface of the electret layer film of the field balance electret layer generate a balanced electrostatic field.

[0090] In the present invention, when the surface of the field-balancing electret layer film on the integrated shielding electrode has a polarization charge with a polarity opposite to that of the electric-field-excited electret layer film, the balanced electrostatic field is consistent with the direction of the strong electrostatic field of the electric-field-excited electret layer film, which plays an auxiliary enhancement role in the alternating pulse electric field; when the surface of the field-balancing electret layer film on the integrated shielding electrode has a polarization charge with the same polarity as that of the electric-field-excited electret layer film, a space charge confinement region can be formed inside the insulating medium to be tested.

[0091] Among them, the space charge confinement region can be controlled by adjusting the size of the field balance electret field.

[0092] Specifically, the non-contact test includes an integral test, and the integral test includes the following steps:

[0093] Step 101: polarizing the electret layer film on the electric field excited electret layer, so that polarized charges are generated on the surface of the electret layer film, and obtaining a first polarized charge density.

[0094] Specifically, the electric field excited electret layer film is polarized by high energy ray ionization or corona discharge, so that the surface of the electret layer film has polarized charge, and the surface potential of the electret after polarization is measured by a surface potential meter, based on which the first polarization charge density is calculated.

[0095] Step 102: placing the insulating medium to be tested on the electret film surface of the field balance electret layer, adjusting the distance between the electric field excitation electret layer and the insulating medium to be tested, and obtaining the distance between the upper surface of the insulating medium to be tested and the lower surface of the field balance electret layer.

[0096] Specifically, first, the insulating dielectric material to be tested is cut to a suitable size and its thickness is measured; then, the insulating dielectric material to be tested is placed on the surface of the field balance electret layer film so that the two fit tightly; finally, the fine-tuning knob of the mobile platform is adjusted to adjust the distance between the electric field excitation electret layer and the insulating dielectric to be tested, and the distance between the upper surface of the insulating dielectric to be tested and the lower surface of the field balance electret layer is measured.

[0097] Step 103: Using a low-voltage pulse generator and a piezoelectric vibration element, an excitation electric field excites the electret layer to vibrate, thereby generating an alternating pulse electric field.

[0098] Specifically, a low-voltage pulse generator is electrically connected to a piezoelectric driving element. As the piezoelectric driving element vibrates, the electric field excites the electret layer to vibrate at a high frequency, and the polarized charges generate an alternating pulse electric field under high-frequency motion.

[0099] Step 104: The space charge in the insulating medium to be measured generates an acoustic pressure wave through the alternating pulse electric field, and the space charge signal window in the insulating medium to be measured is determined on the oscilloscope through the acoustic pressure wave signal.

[0100] Specifically, the space charge in the insulating medium to be tested is disturbed under the action of the alternating pulse electric field to generate acoustic pressure waves. The acoustic pressure waves at different positions in the insulating medium to be tested are transmitted to the piezoelectric sensor at different times. The acoustic pressure waves generated by the space charge close to the piezoelectric sensor are received first. On the oscilloscope, the space charge signal window in the insulating medium to be tested can be determined by the acoustic pressure wave signal generated by the interface induced charge sensed on the field balance electret layer film.

[0101] Step 105: The data collected by the oscilloscope is transmitted to a computer, and the computer analyzes and processes the collected signals to obtain the distribution information of the overall space charge of the insulating dielectric material.

[0102] Specifically, the data collected by the oscilloscope is transmitted to the computer through serial communication, and the computer analyzes and processes the collected signals to obtain the distribution information of the overall space charge of the insulating dielectric material.

[0103] Specifically, the on-off sequence between different piezoelectric sensors and the preamplifier is controlled by the on-off of a multi-way control switch, thereby achieving three-dimensional measurement of the overall space charge of the insulating medium to be measured.

[0104] Furthermore, the non-contact test also includes a layered scanning and reconstruction test, and the layered scanning and reconstruction test includes the following steps:

[0105] Step 201: polarizing the electret layer film on the electric field excited electret layer, so that polarized charges are generated on the surface of the electret layer film, and obtaining a first polarized charge density.

[0106] Specifically, the electric field excited electret layer film is polarized by ray ionization or corona discharge so that the surface of the electret layer film has polarized charge, and the surface potential of the electret after polarization is measured by a surface potential meter, based on which the first polarization charge density is calculated.

[0107] Step 202: polarizing the electret layer film on the field balance electret layer to generate polarized charges on the surface of the electret layer film to obtain a second polarized charge density.

[0108] Specifically, the field-balanced electret layer film is polarized by high-energy ray ionization or corona discharge, so that the surface of the electret layer film has polarized charge, and the polarity is opposite to that of the electric field excited electret layer film. The surface potential of the polarized electret is measured by a surface potential meter, and the second polarization charge density is calculated based on it.

[0109] Step 203: placing the insulating medium to be tested on the electret film surface of the field balance electret layer, adjusting the distance between the electric field excitation electret layer and the insulating medium to be tested, and obtaining the distance between the upper surface of the insulating medium to be tested and the lower surface of the field balance electret layer.

[0110] Specifically, the insulating dielectric material to be tested is first cut to a suitable size and its thickness is measured; then the insulating dielectric material to be tested is placed on the surface of the field-balanced electret layer film so that the two fit tightly; finally, the fine-tuning knob of the mobile platform is adjusted to adjust the distance between the electric field-excited electret layer and the insulating dielectric to be tested, and the distance between the upper surface of the insulating dielectric to be tested and the lower surface of the field-balanced electret layer is measured.

[0111] Step 204: Calculate the zero-field intensity interface position inside the insulating medium to be tested.

[0112] Specifically, the zero-field intensity interface position inside the insulating dielectric material to be tested under the combined action of the electrostatic field of the polarized charges of the electric field-excited electret layer and the field-balanced electret layer thin film is calculated.

[0113] Step 205: Using a low-voltage pulse generator and a piezoelectric vibration element, an excitation electric field excites the electret layer to vibrate, thereby generating an alternating pulse electric field.

[0114] Specifically, a low-voltage pulse generator is electrically connected to a piezoelectric driving element. As the piezoelectric driving element vibrates, the electric field excites the electret layer to vibrate at a high frequency, and the polarized charges generate an alternating pulse electric field under high-frequency motion.

[0115] Step 206: Generate an acoustic pressure wave between the upper surface of the insulating medium to be tested and the zero field strength interface position through an alternating pulse electric field, and determine the space charge signal window in the insulating medium to be tested through the acoustic pressure wave signal on an oscilloscope.

[0116] Specifically, considering the influence of the zero field strength interface, the action area of ​​the alternating pulse electric field is limited to between the zero field strength interface and the upper surface of the insulating dielectric material to be tested. Only the space charges located in this area can be disturbed under the action of the alternating pulse electric field to generate acoustic pressure waves. The acoustic pressure waves at different positions take different times to be transmitted to the piezoelectric sensor in the insulating medium to be tested. The acoustic pressure waves generated by the space charges close to the piezoelectric sensor are received first.

[0117] Step 207: The data collected by the oscilloscope is transmitted to a computer, and the computer analyzes and processes the collected signals to obtain the distribution information of the overall space charge of the insulating dielectric material.

[0118] Specifically, the data collected by the oscilloscope is transmitted to the computer through serial communication, and the computer analyzes and processes the collected signals to obtain the distribution information of the local space charge of the insulating dielectric material.

[0119] Step 208: Control the on-off sequence between different piezoelectric sensors and the preamplifier by turning on and off the multi-way control switch to achieve three-dimensional measurement of the local space charge of the insulating medium to be measured.

[0120] Specifically, the on-off sequence between different piezoelectric sensors and preamplifiers is controlled by on-off of a multi-way control switch, thereby realizing three-dimensional measurement of the local space charge of the insulating dielectric material to be measured.

[0121] Step 209: reducing the second polarization charge density of the electret layer film on the field balance electret layer to adjust the zero field intensity interface position.

[0122] Specifically, the polarization charge density of the field-balancing electret layer thin film is reduced, and the position of the zero-field intensity interface is adjusted to move toward the direction close to the field-balancing electret layer.

[0123] Step 210: Repeat steps 201 to 209 to test the space charge in the entire insulating medium to be tested.

[0124] Step 211: Reconstruct the space charge information of each layer through a computer to obtain the distribution information of the space charge of the insulating medium to be tested.

[0125] Specifically, the space charge information of each layer is reconstructed by a computer to obtain complete and true space charge distribution information of the insulating medium to be tested.

[0126] Furthermore, in the present invention, the computer analyzes and processes the collected signals, including the following steps:

[0127] Step S1: Acquire the collected signal and calculate the transfer function of the test system; Step S2: Calculate the attenuation dispersion coefficient of the acoustic pressure wave in the insulating dielectric material to be tested; Step S3: Calculate the zero field strength position appearing in the insulating medium to be tested based on the polarization charge density of the field-balanced electret layer film; Step S4: Calculate the intensity of the alternating pulse electric field and the attenuation coefficient of the pulse electric field; Step S5: Acquire the measured signal; Step S6: Perform deconvolution recovery processing to obtain preliminary spatial charge information; Step S7: Perform acoustic wave attenuation dispersion recovery and pulse field intensity attenuation recovery to obtain layered spatial charge parameter information; Step S8: Acquire the spatial charge information of each layer and reconstruct the distribution information of all spatial charges of the insulating medium.

[0128] The specific operation process can be described as follows: after the program starts, a reference waveform of the voltage signal corresponding to the insulating medium to be tested under the action of the alternating pulse electric field is obtained without the accumulation of spatial charge; then the reference waveform data is preprocessed by averaging and zeroing to remove signal glitches; the system transfer function of the measuring device is calculated according to the actual output of the system and the known input conditions; the acoustic wave attenuation dispersion coefficient of the sample is calculated according to the acoustic properties of the insulating medium sample to be tested and the actual system output; the zero field strength interface is calculated according to the polarization charge density of the electric field excitation electret layer and the field balance electret film, and the effective test area for the actual test is determined; the field strength attenuation coefficient of the alternating pulse electric field is calculated according to the dielectric properties, thickness and air gap size of the insulating medium sample to be tested. Furthermore, the insulating medium to be tested containing space charge is tested to obtain the measured waveform of the output voltage signal of the piezoelectric sensor; the measured waveform data to be restored are selected for preprocessing, and the signal distortion is corrected by deconvolution processing; the space charge distribution in a predetermined stratified area of ​​the insulating medium sample to be tested is obtained by acoustic wave attenuation dispersion recovery, pulse field intensity attenuation recovery and inverse Fourier transform; all stratified space charge information is reconstructed to obtain the complete space charge distribution information of the insulating medium to be tested; finally, the data is classified, stored and displayed.

[0129] The present invention can realize the overall test and layered scanning reconstruction test of the space charge in the insulating medium to be tested; because the alternating pulse electric field at the upper surface of the insulating medium to be tested is larger than that at other positions, the present invention is extremely sensitive to the test of the outer layer and shallow surface space charge of the insulating medium to be tested; in addition, the low-power, non-contact device configuration of the present invention is more effective for the space charge test of the insulating medium of the spacecraft.

[0130] The present invention has universal applicability to the space charge test of the insulating dielectric material to be tested, and has significant advantages in the space charge test of the insulating dielectric of the spacecraft protection layer and the shallow surface space charge test of the insulating dielectric material.

[0131] The present invention forms a strong electrostatic field in a direction perpendicular to the surface of the electret layer by presetting an electric field to excite the polarized charges on the surface of the electret layer. With the high-frequency vibration of the electret layer, the polarized charges generate an alternating pulse electric field under high-frequency motion, and the space charges in the insulating medium to be measured are disturbed under the action of the alternating pulse electric field to form an acoustic pressure wave. When the surface of the field-balanced electret layer film on the integrated shielding electrode has polarized charges with the same polarity as the electric-field-excited electret layer film, the balanced electrostatic field and the strong electrostatic field of the electric-field-excited electret layer film are in opposite directions, and the interaction between the two electrostatic fields forms a zero-field strength interface at a certain position inside the insulating medium to be measured. The existence of the zero-field strength interface prevents the action of the alternating pulse electric field from crossing the zero-field strength interface to reach other positions of the insulating medium material to be measured, and only the space charges in the non-confined area under the action of the alternating pulse field can generate an acoustic pressure wave, thereby realizing layered scanning and reconstruction of the original space charges in the insulating medium to be measured. Furthermore, the array distribution of the piezoelectric sensor can realize three-dimensional measurement of the space charge of the insulating medium material to be measured. The present invention essentially removes the electric field excitation electrodes and high-voltage electric pulse devices in the traditional PEA test device, avoids the interface effect and surface discharge between the insulating medium to be tested and the electric field excitation electrodes, and realizes the non-contact configuration of the space charge test device; realizes the targeted test of the real space charge in a specific area of ​​the insulating material to be tested under low power and low voltage drive, breaks through the limitation of the thinking that space charge test can only be performed under high-voltage electric pulse excitation, and has the ability to perform layered testing of the space charge of the insulating medium to be tested, and has the characteristics of low voltage, non-contact, layered reconstruction, array, high applicability, etc.

[0132] The technical problems solved by the present invention are:

[0133] 1. The present invention eliminates the excitation electrode (or power-on stage) and high-voltage electric pulse generating device in the traditional PEA test device, thus avoiding the hazards such as interface effect, surface discharge and dielectric breakdown between the insulating medium sample and the excitation electrode.

[0134] 2. The present invention eliminates complicated high-voltage insulation devices and realizes the miniaturization of the test device; realizes low-voltage driving of the electret layer to generate a high-field strength alternating pulse field; realizes non-contact testing of the space charge of the insulating medium; realizes the testing of the shallow surface space charge of the insulating medium; and realizes the layered scanning and reconstruction of the original space charge in the insulating medium.

[0135] 3. The present invention has the ability to adapt to the space environment to test the space charge of the insulating medium of the spacecraft protective layer, and has the characteristics of low voltage drive, non-contact testing, layered scanning reconstruction and high applicability.

[0136] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A space charge non-contact testing system, characterized in that: The system comprises: a substrate, a mobile platform, a bracket, a piezoelectric driving element, an electric field excitation electret layer, an insulating medium to be tested, a field balance electret layer, a piezoelectric sensor array, an absorbing material layer, a multi-way control switch, a preamplifier, an integrated shielding electrode, a low-voltage pulse generator, an oscilloscope and a computer; One end of the substrate is mechanically connected to the mobile platform, and the substrate is parallel to the upper surface of the insulating medium to be tested; the upper surface of the piezoelectric driving element is mechanically connected to the substrate and vibrates under the electrical excitation of the low-voltage pulse generator; the electric field excitation electret layer is mechanically insulated and connected to the lower surface of the piezoelectric driving element, and an alternating pulse electric field is generated under the excitation of the piezoelectric driving element; the field balance electret layer is spin-coated on the upper surface of the integrated shielding electrode, which is used to place the insulating medium to be tested and form a balanced electric field; the piezoelectric sensor array is equidistantly placed on the lower surface of the integrated shielding electrode, which is used to receive the acoustic pressure waves induced by the space charge of the insulating medium to be tested under the action of the alternating pulse field generated by the electric field excitation electret layer The signal is converted into an electrical signal; the absorbing material layer is used to absorb the acoustic pressure wave signal passing through the piezoelectric sensor array to reduce reflection; the multi-way control switch is used to control the on-off sequence between a single piezoelectric sensor and the preamplifier; the preamplifier is placed inside the integrated shielding electrode and is electrically connected to the piezoelectric sensor array to amplify the electrical signal data output by the piezoelectric sensor; the oscilloscope is electrically connected to the preamplifier to collect and display the amplified electrical signal data and transmit it to the computer through the serial port; the computer analyzes, processes and reconstructs the collected electrical signal data to obtain the spatial charge distribution information of the insulating medium.

2. The space charge non-contact testing system according to claim 1, characterized in that: The distance between the substrate and the surface of the insulating medium to be tested is adjusted by moving the platform.

3. The space charge non-contact testing system according to claim 1, characterized in that: The electric field excitation electret layer is used as an alternating pulse electric field source to induce space charge to generate acoustic pressure waves, including a back electrode and an electret layer film spin-coated on the back electrode using micro-nano technology, and the surface of the electret layer film has polarized charges.

4. The space charge non-contact testing system according to claim 1, characterized in that: The array distribution of piezoelectric sensors realizes the three-dimensional measurement of the space charge of the insulating medium to be measured.

5. The space charge non-contact testing system according to claim 1, characterized in that: The field-balancing electret layer is spin-coated on the upper surface of the integrated shielding electrode using a micro-nano process, and is used to place the insulating medium to be tested and form a balanced electric field to confine the space charge layer to be tested.

6. A space charge non-contact testing method, characterized in that: Applicable to the space charge non-contact testing system of claim 1, the method comprising: Step 1: Using a first pulse voltage to drive the electric field on the insulating medium to be tested to excite the electret layer to vibrate and generate an alternating pulse field, so that the space charge in the insulating medium to be tested generates an acoustic pressure wave, thereby realizing a non-contact test of the space charge inside the insulating medium to be tested; Step 2: A balanced electrostatic field in the opposite direction to the alternating pulse field is formed by placing a field-balancing electret layer under the insulating medium to be tested, thereby forming a zero-field strength interface inside the insulating medium to be tested, thereby realizing a layered scanning reconstruction of the space charge inside the insulating medium to be tested.

7. The space charge non-contact testing method according to claim 6, characterized in that: The polarization charges on the surface of the electret film of the field-balancing electret layer generate a balanced electrostatic field.

8. The space charge non-contact testing method according to claim 6, characterized in that: The non-contact test includes an integral test, which includes: Step 101: polarizing the electret layer film on the electric field excited electret layer, so that polarized charges are generated on the surface of the electret layer film, and obtaining a first polarized charge density; Step 102: placing the insulating medium to be tested on the electret layer film surface of the field balance electret layer, adjusting the distance between the electric field excitation electret layer and the insulating medium to be tested, and obtaining the distance between the upper surface of the insulating medium to be tested and the lower surface of the field balance electret layer; Step 103: Using a low voltage pulse generator and a piezoelectric vibration element, an electric field is excited to excite the electret layer to vibrate, thereby generating an alternating pulse electric field; Step 104: The space charge in the insulating medium to be tested generates an acoustic pressure wave through the alternating pulse electric field, and the space charge signal window in the insulating medium to be tested is determined on the oscilloscope through the acoustic pressure wave signal; Step 105: The data collected by the oscilloscope is transmitted to a computer, and the computer analyzes and processes the collected signals to obtain the distribution information of the overall space charge of the insulating dielectric material.

9. The space charge non-contact testing method according to claim 8, characterized in that: The on-off sequence between different piezoelectric sensors and the preamplifier is controlled by the on-off of a multi-way control switch, so as to realize the three-dimensional measurement of the overall space charge of the insulating medium to be measured.

10. The space charge non-contact testing method according to claim 6, characterized in that: The non-contact test includes a layered scanning and reconstruction test, and the layered scanning and reconstruction test includes: Step 201: polarizing the electret layer film on the electric field excited electret layer, so that polarized charges are generated on the surface of the electret layer film, and obtaining a first polarized charge density; Step 202: polarizing the electret layer film on the field balance electret layer to generate polarized charges on the surface of the electret layer film, thereby obtaining a second polarized charge density; Step 203: placing the insulating medium to be tested on the electret layer film surface of the field balance electret layer, adjusting the distance between the electric field excitation electret layer and the insulating medium to be tested, and obtaining the distance between the upper surface of the insulating medium to be tested and the lower surface of the field balance electret layer; Step 204: Calculate the zero-field intensity interface position inside the insulating medium to be tested; Step 205: Using a low voltage pulse generator and a piezoelectric vibration element, an excitation electric field excites the electret layer to vibrate, thereby generating an alternating pulse electric field; Step 206: generating an acoustic pressure wave between the upper surface of the insulating medium to be tested and the zero field strength interface position by means of an alternating pulse electric field, and determining a space charge signal window in the insulating medium to be tested by means of the acoustic pressure wave signal on an oscilloscope; Step 207: The data collected by the oscilloscope is transmitted to a computer, and the computer analyzes and processes the collected signals to obtain the distribution information of the overall space charge of the insulating dielectric material; Step 208: controlling the on-off sequence between different piezoelectric sensors and the preamplifier by turning on and off the multi-way control switch to achieve three-dimensional measurement of the local space charge of the insulating medium to be measured; Step 209: reducing the second polarization charge density of the electret layer film on the field balance electret layer to adjust the zero field intensity interface position; Step 210: Repeat steps 201 to 209 to test the space charge in the entire insulating medium to be tested; Step 211: Reconstruct the space charge information of each layer through a computer to obtain the distribution information of the space charge of the insulating medium to be tested.

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